Hard Disk Drives (HDDs) remain popular storage devices due to their large capacity and low cost. Although non-volatile flash-based Solid State Drives (SSDs) have attracted considerable attentions for their ability to replace HDDs in many applications, they are more expensive than HDDs, especially as storage capacity increases. In addition, the digital data explosion demands a huge amount of storage space, especially for backup and archives. These facts ensure that HDDs still retain their own merits against SSDs and serve as an important component in diverse applications. Thanks to advances in recording technology, manufacturing, and materials, drive capacity has grown by nearly six orders of magnitude in the last fifty years. However, magnetic HDDs are increasingly nearing a density limit imposed by the super-paramagnetic effect for perpendicular recording. While current drives store 400 GB/in2, the current limit is estimated to be about 1 TB/in2. As a result, new approaches are needed to ensure that disk density continues to improve. One such approach has been developed in the form of shingled drives, such as Shingled Magnetic Recording (SMR) drives, which can achieve much higher data density than more conventional magnetic HDDs. Shingled drives offer minimal changes to disk hardware and recording technology, but they also have very limited or non-existent ability to perform random writes.
To improve storage density over traditional magnetic drives, shingled drives use a write head with a stronger, but asymmetric, magnetic field to overlap the currently written track with the previous track, leaving only a relatively small strip of the previous write track untouched. While this smaller strip is a fraction of the feasible write size, it is still sufficiently large to be read with current Giant Magneto-Resistive (GMR) read heads, which do not require as strong of a magnetic field as write heads. As a result, shingled writing can place readable tracks closer together and increase data density within tracks themselves, further extending the limits of perpendicular magnetic recording.